1. Field of the Invention
The present invention relates to a release device which may to release such items as antennas, solar arrays, positioning mechanisms, and other devices.
2. Description of Related Art
A release apparatus, such as a separation spool device, is used to release a captured member which constrains the deployment of a spacecraft element, such as a solar array and/or reflectors, in the stowed position. In many prior art devices, the spacecraft element was restrained with a wire or a holddown rod system which was released using a pyrotechnic device. Typically, the pyrotechnic device would fire a blade against a base, with the wire or rod to be cut and released. Although useful in many applications, these devices imparted high shock loads into the units which they were to release, as well as the spacecraft itself.
A design that avoided the shocks associated with pyrotechnic release devices was the separation spool device, which used a fused element to release a captured member. U.S. Pat. No. 6,133,818, to Baghdasarian, discusses a release apparatus wherein two piece split spool with an annulus is used to capture a capture member larger in diameter than the annulus of the spool. The two pieces of the split spool are held together with a wire that is wrapped around the spool. A drawback of this design is that the wire, wrapped under tension around the outside of the spool, may have unpredictable dynamics in some cases when released. In some cases, there may be risk of the wire fouling upon itself when released, which may prevent the spool from spreading far enough apart to allow the captured member to pass through, and thus this may prevent the release device from releasing the stowed spacecraft element. Another drawback of this design is that a two piece spool design presents a geometry that requires significant radial movement of the spool pieces to affect the release.
Further, a two segment spool has geometric limitations as far as load carrying capacity and a phenomenon referred to as “Friction lock up” condition, a failure to release condition due to friction between the spool-to-captured member interface, and the fact that spherical (ball) end of the captured member leaves the segments contacting the two extreme points of each segment. These two points are almost 180 degrees apart for a 2-segment spool. A ball end could easily be prevented from release with very little friction between the ball and the spool interface.
What is called for is a capture spool release device that overcomes the potentially unstable dynamics of wire wrapped spool and the drawbacks of a two segment separation device. What is also called for is a split spool that minimizes the travel required of a spool element in order to affect a release of the captured member.